External hemorrhoids become hard in no more than two ways, the first being the formation of an acute thrombus in the external hemorrhoid, and the second being inflammation of the external hemorrhoid with local edema. Both cases are accompanied by pain in the nucleus of the external hemorrhoid. In either case, if there is inflammation you can treat it symptomatically with appropriate antibiotics, then topical hemorrhoid cream and daily warm water sitz baths. If it is a thrombosis, you can take oral medication to improve circulation, along with topical hemorrhoid cream, and then a daily sitz bath with warm water or warm salt water. If the symptoms are more severe and conservative medication is not effective, further surgical treatment should be considered, which requires removal of the external hemorrhoid or thrombectomy.